1. Field of the Invention
The present invention relates to a flexible manufacturing system provided with a machine tool for machining workpieces to form finished products, racks for storing a plurality of workpieces, blank materials and finished products, a transfer device for transferring blank materials and workpieces between the machine tool and the racks, and a control apparatus for controlling the transfer operation of the transfer device. Further, the present invention relates to a control method for the flexible manufacturing system.
2. Discussion of the Related Art
As flexible manufacturing systems (hereafter referred to as “FMSs”) capable of a wide-variety and small-quantity production, there has been known one which is described in JP 6-63852 A for example. This Japanese application describes a system provided with machine tools for machining workpieces, a rack for storing pluralities of workpieces, blank materials and finished products, setting stations where workers perform setting operations, and a transfer device movable between these facilities. The Japanese application further describes at paragraphs [0012] and [0013] that at each setting station, the worker attaches ante-machining workpieces (hereafter referred to as “blank materials”) to a pallet or detaches post-machining workpieces (hereafter referred to as “finished products”) from another pallet.
More specifically, the worker performs operations at each setting station as follows. In attaching blank materials to a pallet, the worker instructs the transfer device to transfer a blank material basket containing the blank materials from the rack to the setting station and at the same time, to transfer from the rack a pallet to which the blank materials are to be attached. Then, at the setting station, the worker moves the blank materials from the blank material basket to the pallet. Further, in detaching finished products from a pallet and storing them in a finished product basket, the worker instructs the transfer device to transfer the pallet with finished products attached thereto from the rack to the setting station and, at the same time, to transfer from the rack a finished product basket into which the finished products are to be put.
In the FMSs of this kind, it has been a practice to place the machining order of workpieces in machine tools under a schedule control. Thus, automatic assignments or determinations are made of the order in which pallets with workpieces attached thereon are transferred from a rack to each machine tool as well as of respective times at which such transfers are carried out. However, as mentioned earlier, the workers are required to give instructions in attaching blank materials contained in a blank material basket to a pallet and in detaching finished products from a pallet to move them to a finished product basket. More specifically, in attaching blank materials to a pallet, the worker at a setting station checks the pallet after the same is transferred to the setting station, then searches for a blank material basket containing blank materials to be attached to the pallet and instructs the transfer of the blank material basket to the setting station. In this operation, the time is taken for the worker to search for the blank material basket. Therefore, for the purpose of improving the efficiency of the system operation, it has been required to shorten such search time.
Further, it has heretofore been a practice in FMSs that finished products are not controlled on a basis of a lot which is a manufacturing unit of products. Thus, once blank materials are charged into an FMS, only the kind of each blank material is grasped, and each finished product is discharged without taking account of the lot to which it belongs. That is, it has been a practice that finished products different in lot are put in mixture into each finished product basket. However, the need for controlling finished products on a lot-by-lot basis has been proposed by the users in terms of traceability.